This invention relates to a corner bracket for use in a sectional shelf which is detachably assembled from shelf boards and struts.
Normally, a sectional shelf is formed by arranging four struts each made of an angle steel member at four corners of a rectangular contour, and joining a shelf board made of thin steel plate with these struts. In order to strengthen the joint portion between the struts and the shelf board, a corner bracket is normally mounted at each joint portion of the strut and the shelf board.
FIG. 35 is a perspective view showing a state where the conventional corner bracket used for the above purpose is mounted between the strut and the shelf board. The corner bracket 23 includes wing members. An angle formed by the two wing members is substantially 90.degree.. Each wing member is formed into a triangular figure, and has an insertion hole defined at each of three corner portions thereof. Insertion holes corresponding to these insertion holes of the wing member are defined in each of a side wall 24 of a strut 21 and a side board 25 of a shelf board 22.
A bolt is inserted through these insertion holes, and an unillustrated nut is spirally fitted to the bolt. In this way, the strut 21 and the shelf board 22 are joined with each other. In other words, there is realized a three-point engaging structure which is strong dynamically. With this structure, the strut 21 and the shelf board 22 are positioned reliably perpendicular to each other, thereby preventing effectively the sectional shelf from deforming upon being subjected to an external force.
Further as shown in FIG. 36, there are cases where a planer triangular member is used as a corner bracket 23. In this corner bracket 23 are defined three insertion holes similar to the wing member of the corner bracket shown in FIG. 35. This corner bracket 23 is also mounted between the side wall 24 of the strut 21 and the side board 25 of the shelf board 22, and these three members are integrally joined with one another by a bolt.
Each of these corner brackets 23 has three engaging portions per wing member thereof: a common engaging portion for joining the strut 21, the shelf board 22, and the corner bracket 23 with one another; a board engaging portion for joining the corner bracket 23 with the shelf board 22; and a strut engaging portion for joining the corner bracket 23 with the strut 21. The common engaging portion and the board engaging portion are arranged in a horizontal direction. The common engaging portion and the strut engaging portion are arranged in a vertical direction. A portion of the wing member between the strut engaging portion and the board engaging portion acts dynamically as a clamp against the external force subjected to the shelf board 22.
However, in the conventional corner bracket 23 as described above, a hypotenuse edge portion of the triangular wing member is located inward of a line connecting the strut engaging portion and the board engaging portion (hereinafter referred to as a clamping line). Thus, when a heavy article is placed on the shelf board 22 or a horizontally acting force is subjected to the shelf board 22 in a state where the corner brackets 23 are mounted on the joint portions of the struts 21 and the shelf board 22 and the bolts are inserted through the aforementioned insertion holes to join the struts 21 with the shelf board 22, the stress concentrates on the hypotenuse edge portions of the corner brackets 23.
If the hypotenuse edge portion of the corner bracket 23 resisting against the bending moment subjected to the shelf board 22 is located inward of the clamping line between the strut engaging portion and the board engaging portion, the bending load is entirely applied to the hypotenuse edge portion and the stress concentrates thereon. Accordingly, the corner bracket is deformed unless having sufficient rigidity, with the result that the sectional shelf may incline in a certain direction.